Study On Mineralization Of Epithermal Gold Deposits In Eastern Heilongjiang, China

The Sishanlinchang gold-silver deposit and the Sipingshan gold deposit are two typical epithermal gold deposits occurring in eastern Heilongjiang province of China, which respectively locates at Jidong county and Hulin county in Mudanjiang city. The main ore of the Sishanlinchang gold-silver deposit is the gold-bearing quartz vein,which contains a lot of various sulfides and has a higher Au grade. The geochemical study indicates that various rocks in the deposit are all rich in ore-forming elements and Au is closely correlative with As、Pb、Ag and Cu. In addition, the gold-bearing quartz vein is characterized by strong enrichment in Rb、U、Zr、Hf and slightly enrichment in Ba、Th、K and remarkable depletion in Ti. The REEs of the deposit relatively enriched in HREEs and depleted in LREEs,which have a dextral-inclined chondrite-normalized patterns and a slightly negative Eu anomaly. Theδ34S values of the deposit are -1.8‰～+5.0‰, which indicates a unique deep-seated sulfur source for the deposit. And the Pb isotopic compositions of the sulfides and rocks in the deposit plot between mantle evolution curve and orogenic belt evolution curve in Zartman’s Pb diagram,suggesting a mixed crust-mantle Pb source for the deposit. The fluid inclusion study shows that the ore-forming fluid is mainly composed of H2O、Na+ and Cl-, and its temperature and salinity are 215～350℃and 3.87%～10.87% respectively. The hydrogen and oxygen isotopic compositions of quartz are -79.0～-118.8‰and 4.70～5.69‰, respectively. It shows that the ore-forming fluid is derived from both the magmatic fluid and meteoric water. In a word, the Sishanlinchang gold-silver deposit is precipitated in fault zone by the ore-forming fluid which formed by magmatic fluid and meteoric water. The Sipingshan gold deposit hosted in the volcanic basin upside the late Cretaceous rhyolite porphyry, and the gold-bearing chert is the main ore,which relatively lacks sulfides and has a low Au grade. The geochemical study indicates that the content of the ore-forming elements in the deposit are all low, and Au is correlative with Ag、Cu、Pb、As and Hg. The upper chert and the lower chert are all enriched in Rb、Ba、U and highly depleted in Ti compare to primitive mantle. The REEs of the deposit is characterized by low content and dextral-inclined chondrite-normalized patterns which relatively enriched in HREEs and depleted in LREEs. The upper chert has both negative Eu and Ce anomalies, but the lower chert is only with positive Eu anomaly and both the hot spring-cemented breccia and rhyolite porphyry are only with negative Eu anomaly. Theδ34S values of the deposit are -9.8‰～29.7‰, which means that the sulfur of the deposit derived from both the deep-seated magmatic sulfur and terrestrial sulfate sulfur. And the Pb isotopic compositions of the sulfides and rocks mainly plot between upper crust evolution curve and orogenic-belt evolution curve in Zartman’s Pb diagram,also suggesting a mixed crust-mantle Pb source for the deposit. The fluid inclusion study shows that the temperature of the ore-forming fluid are180℃～224℃, and theδD values are -84～-106‰,δ18O values are -3.1～1.3‰, which suggests that the ore-forming fluid is derived from both the magmatic fluid and meteoric water. In short, the Sipingshan gold deposit was precipitated in the near-surface water basin by a hot spring formed by the ore-forming fluid ejecting from erathsurface through tectonic fault zone.